Installation and method for acoustic measurement with marker microphone in space

ABSTRACT

The acoustic measurement installation comprises: 
         acoustic measurement instrumentation ( 3 ) comprising in particular an acoustic measurement antenna ( 4 ) fitted with at least one microphone ( 5 );    a positioning system ( 11 ) for positioning the antenna ( 4 ) by ultrasound, the positioning system comprising: 
           at least one ultrasound emitter ( 12 ) mounted on the antenna at a known distance relative to the microphone; and    an ultrasound receiver base ( 14 ) for receiving the signals emitted by each emitter and adapted to determine the position of each emitter;    
           and a control unit ( 16 ) for controlling the positioning system ( 11 ) for positioning the antenna ( 4 ) and the acoustic measurement instrumentation ( 3 ), the control system being adapted during a first stage to cause each emitter ( 12 ) to emit in succession in order to determine the position of the antenna, and during a second stage to cause the microphones ( 5 ) to perform acquisition in order to implement acoustic measurement using the measurement instrumentation.

The present invention relates to the technical field of acousticmeasurement in the broad sense, in a measurement zone in which positionin three dimensions needs to be known.

More precisely, the present invention relates to the field of measuringan acoustic field coming from a source that can be direct or indirect,single or multiple, said measurement being performed in a zone that isidentified in three dimensions and that is situated in the environmentof the sound source.

A particularly advantageous application of the invention lies inperforming acoustic measurements inside a volume such as a room inside abuilding or transport means (cabin or vehicle) or in the environment ofa sound source such as an engine or a machine.

In numerous fields, there is a need to proceed with acousticmeasurements in order to characterize one or more sound sources, for thepurpose, for example, of limiting the influence thereof, in particular.For example, it is necessary to perform acoustic measurements outside inorder to characterize a (single or multiple) source or inside a vehiclecabin in order to determine the characteristics of the sound field heardin order in particular to limit the effects thereof.

In order to proceed with acoustic measurements, it is known to use anacoustic measurement installation comprising measurement instrumentationhaving an acoustic measurement antenna which is generally fitted with aseries of microphones. Such an acoustic measurement antenna is generallycarried by a robot arm whose position in three dimensions is determinedby measurement sensors.

Such a measurement installation does not give satisfaction in practicesince it is of considerable weight and size and is not suitable for useinside a volume that is restricted or cluttered, such as a vehiclecabin.

The invention thus seeks to remedy the above-mentioned drawbacks byproposing an acoustic measurement installation designed to present smallvolume while also making it possible to pick up accurately and reliablymeasurements of an acoustic field coming from one or more sound sources.

To achieve such an object, the invention provides an acousticmeasurement installation comprising:

-   -   acoustic measurement instrumentation comprising in particular an        acoustic measurement antenna fitted with at least one        microphone;    -   a positioning system for positioning the antenna by ultrasound,        the positioning system comprising:        -   at least one ultrasound emitter mounted on the antenna at a            known distance relative to the microphone; and        -   an ultrasound receiver base for receiving the signals            emitted by each emitter and adapted to determine the            position of each emitter in three dimensions;    -   and a control unit for controlling the positioning system for        positioning the antenna and the acoustic measurement        instrumentation, the control system being adapted during a first        stage to cause each emitter to emit in succession in order to        determine the position of the antenna in three dimensions, and        during a second stage to cause the microphones to perform        acquisition in order to implement acoustic measurement using the        measurement instrumentation.

The invention also seeks to provide a method adapted to perform acousticmeasurements in a zone that is identified in three dimensions with greataccuracy, while still being simple to implement.

To achieve such an object, the acoustic measurement method of theinvention comprises the following steps:

-   -   fitting an acoustic measurement antenna comprising at least one        microphone with at least one ultrasound emitter mounted at a        known distance from the microphone;    -   placing the acoustic measurement antenna in a position that is        stationary relative to the sound source;    -   placing an ultrasound receiver base to face the antenna, the        receiver base being adapted to receive an ultrasound signal        emitted by the ultrasound emitter and to determine the position        of the emitter;    -   causing each ultrasound emitter to emit in succession so as to        enable the ultrasound receiver base to determine the position of        each emitter and consequently of each microphone; and    -   after the end of the stage of causing all of the ultrasound        emitters to emit, controlling the microphones to operate in        acquisition so as to perform the acoustic measurement of the        sound source.

In a variant implementation, the method of the invention furthercomprises the following steps:

-   -   placing a reference structure in a stationary position, the        structure defining at least one reference marker having at least        three points; and    -   causing each ultrasound emitter of an acoustic pointer fitted        with at least two emitters to emit in succession, and to do so        for each position of the pointer placed on each point of the        reference marker so as to enable the positions of the points of        the reference marker to be determined in a frame of reference        associated with the position of the ultrasound receiver base.

According to another characteristic of the invention, the method of theinvention comprises, in addition to the preceding steps, and in order toenlarge the coverage of the acoustic measurement, the following steps:

-   -   moving the ultrasound receiver base to place it in a second        stationary position;    -   causing each ultrasound emitter of the pointer for each position        of the pointer placed on each point of the reference marker to        emit in succession in such a manner as to enable the positions        of the points of the reference marker to be determined in        another frame of reference associated with the second position        of the ultrasound receiver base; and    -   on the basis of the positions of the points of the reference        marker for the first and second positions of the ultrasound        receiver base, determining the positions of the microphones in a        single frame of reference.

Various other characteristics appear from the description below madewith reference to the accompanying drawings which show, as non-limitingexamples, embodiments of the subject matter of the invention.

FIG. 1 is a diagrammatic view showing an example of an application of anacoustic measuring installation in accordance with the invention.

FIG. 2 is a general view of an acoustic measurement antenna forming partof the installation in accordance with the invention.

FIG. 3 is a detail view of the acoustic measurement antenna shown inFIG. 2.

FIG. 4 is a timing chart showing how the acoustic measurementinstallation in accordance with the invention operates.

FIG. 5 is a diagram showing a variant embodiment of the acousticmeasurement installation in accordance with the invention.

As can be seen more clearly in FIG. 1, the present invention relates toan installation 1 for performing an acoustic measurement that needs tobe positioned in three dimensions. Thus, the installation 1 is adaptedto act at a geometrically identified location to pick up the sound fieldthat comes from one or more sound sources directly or indirectly, e.g.because a wall is transparent, because of sound leakage, etc. In aparticularly advantageous manner, the installation 1 is adapted toperform acoustic measurement inside a closed enclosure 2, which in theexample shown is constituted by a vehicle cabin. In this embodiment (andalso in general), the sound source may be a single source (enginenoise), or multiple sources (engine noise together with noise comingfrom outside the cabin and heard inside the cabin). Naturally, theinstallation 1 of the invention may involve other applications such asperforming acoustic measurements inside a dwelling or acousticmeasurements performed in an open or confined environment of a soundsource, such as a machine, for example.

The installation 1 comprises instrumentation 3 for acoustic measurementcomprising in particular an acoustic measurement antenna 4 fitted withat least one microphone, and in the example shown with a series ofmicrophones 5, with the number of microphones depending on the desiredaccuracy, on the frequency range of interest, and on the extent of thezone in which acoustic measurements are to be performed. In conventionalmanner, the microphones 5 are connected to an acoustic measurement unit6 for measuring signals picked up by the microphones 5. The variousprocessing functions of the unit 6 are not described in the descriptionbelow since they are well known and form part of the technical knowledgeof the person skilled in the art.

As can be seen more precisely in FIGS. 2 and 3, the acoustic measurementantenna 4 in the example shown comprises sixty-four microphones 5extending in a plane and distributed over eight columns and eight rows.The microphones 5 are mounted on a support 7 that forms a kind of framewith cross-members. The microphones 5 are connected to the processorunit 6 by a connection 8.

According to a preferred embodiment characteristic, the acousticmeasurement antenna 4 is fitted with a member 9 for holding the antennain position, and in the example shown this is constituted by a holdingand control handle, as explained in the description below. This handle 9which extends from the support 7 thus makes available an antenna 4 thatis of portable nature. The handle 9 is preferably mounted to moverelative to the acoustic measurement antenna 4. For this purpose, thehandle 9 is mounted to move relative to the antenna 4 about a hinge axis10 enabling it to be pivot relative to the support so as to facilitatepositioning the acoustic measurement antenna 4.

The installation 1 also comprises a system 11 enabling the acousticmeasurement antenna 4 to be positioned by an ultrasound method. Thepurpose of this system 11 is to determine the coordinates in threedimensions of the acoustic measurement antenna 4. This positioningsystem 11 comprises at least one, and in the example shown four,ultrasound emitters 12 mounted on the acoustic measurement antenna 4 atknown distances from the microphones 5. It should be understood thateach ultrasound emitter 12 must be placed at a known distance from atleast one microphone 5 insofar as the microphones 5 are separated fromone another by distances that are known. The number of ultrasoundemitters 12 depends on the type of antenna used. Thus, the acousticmeasurement antenna 4 is fitted:

-   -   with an ultrasound emitter 12 when the antenna 4 comprises one        microphone 5;    -   with at least two ultrasound emitters 12 when the antenna 4        comprises a series of microphones 5 disposed linearly;    -   with at least three ultrasound emitters 12 when the antenna 4        comprises a series of microphones 5 disposed in a plane; and    -   with at least four ultrasound emitters 12 when the antenna 4        comprises a series of microphones 5 disposed in a volume.

In the example shown, the acoustic measurement antenna 4 is plane and isfitted with four ultrasound emitters 12, as a safety precaution in theevent of one of the emitters 12 being masked.

The installation 1 also comprises an ultrasound receiver base 14 forreceiving the signals emitted by each of the ultrasound emitters 12.This ultrasound receiver base 14 is also adapted to determine theposition in three dimensions of each ultrasound emitter 12, andconsequently the position in three dimensions of the microphones 5, ormore generally of the antenna 4. In known manner, this base 14 uses adirection finding or interferometric method to determine the positionsin three dimensions of the ultrasound emitters 12. To this end, the base14 is fitted with at least three ultrasound receivers and with processorand calculator means for determining the positions in three dimensionsof the ultrasound emitters 12, and consequently of the antenna 4.

It should be observed that the accuracy with which the antenna 4 ispositioned depends directly on the position of the ultrasound receiverbase 4 in the beams from the emitters 12. Typically, best accuracy foremitter position is obtained when the base 14 lies on the axis of theemitter 12. Thus, according to a preferred characteristic of theinvention, each ultrasound emitter 12 is mounted on the antenna 4 on amoving support 71 enabling the axis of the emitter 12 to be adjustedrelative to the ultrasound receiver base. The moving support 71 which isconstituted in the form of a cardan joint, enables the axis of eachemitter 12 to be adjusted in two planes.

The installation 1 also comprises a control unit 16 for controlling thepositioning system 11 and the acoustic measurement instrumentation 3.This control unit 16 includes means adapted, during a first stage T₁(FIG. 4), to cause each emitter 12 to emit in succession so that thebase 14 can determine the position of the antenna 4. At the end of thisfirst stage T₁, during a second stage T₂, the unit 16 causes themicrophones 5 to operate in acquisition in order to perform the acousticmeasurements using the acoustic measurement unit 6. The positions of themicrophones 5 as determined by the ultrasound receiver base 14 aredelivered to the measurement unit 6 so that the geometrical position ofeach microphone 5 is known and delivered to the acoustic measurementunit 6.

The acoustic measurement installation 1 of the invention operates in amanner that stems directly from the above description. The acousticmeasurement method described below relates to performing acousticmeasurements inside a motor vehicle cabin 2. Naturally, the method ofthe invention can be applied in measurement situations that are notconfined (in an open medium).

The acoustic measurement antenna 4 is placed in a position that is fixedrelative to the sound source. For example, the acoustic measurementantenna 4 is held in a position by an operator carrying the antenna 4 bymeans of its handle 9. The ultrasound receiver base 14 is placed facingthe antenna 4 in a relationship that enables it to be “seenacoustically”. The ultrasound receiver base 14 is thus adapted toreceive an ultrasound signal as emitted by each ultrasound emitter 12mounted at known distance from the microphone(s) 5 fitted to theacoustic measurement antenna 4. As can be seen more precisely from FIG.4, the method consists in causing each of the ultrasound emitters 12(referenced by references 12 ₁, 12 ₂, 12 ₃, 12 ₄) to emit in successionto enable the ultrasound receiver base 14 to determine the position ofeach ultrasound emitter, and consequently of each microphone 5. For thispurpose, the operator causes each ultrasound emitter 12 to emit, e.g. byusing a control button 17 placed on the handle 9. Once the ultrasoundreceiver base 14 has determined the position of the first ultrasoundemitter 12, a signal is emitted to stop emission from the ultrasoundemitter 12. The operator then causes the second ultrasound emitter 12 toemit so that the ultrasound receiver base 14 can determine its position.This operation is repeated for each of the ultrasound emitters 12, i.e.all four of them in the example shown.

At the end of this first stage T₁, the positions in three dimensions ofthe ultrasound emitters 12, and consequently of the microphones 5 areknown. The second stage T₂ of the method consists in acquiring acousticsignals (in the audible band) using the microphones 5. For this purpose,the operator causes the microphones 5 to operate in acquisition, e.g. bypressing a control button 18 placed on the handle 9, thereby performingacoustic measurement of the sound source.

The acoustic measurement instrumentation 3, and in particular theprocessor means 6 serve to pick up and process the signals sensed byeach microphone 5, whose position in three dimensions is known anddetermined by the ultrasound receiver base 14.

It should be observed that the two above-described stages are performedwhile maintaining the acoustic measurement antenna 4 and the ultrasoundreceiver base 14 in fixed positions. Naturally, these two stages maysubsequently be repeated for other possible positions of the acousticmeasurement antenna 4. Putting the antenna 4 in different zones in threedimensions enables the acoustic field to be picked up in different zonesat a distance from the ultrasound receiver base 14. Nevertheless, itshould be observed that the acoustic measurement antenna 4 must alwaysbe placed so as to be “acoustically in sight” of the ultrasound receiverbase 14 (i.e. “in sight” in terms of range and angular aperture of theultrasound beams).

FIG. 5 shows an embodiment in which the space for performingmeasurements, i.e. for positioning the antenna 4 is increased. In thisvariant, the installation 1 comprises a system 20 for positioning theultrasound receiver base 14. Such a positioning system 20 comprises afixed reference structure 21 defining at least one reference markerhaving at least three points P_(i). Such a positioning system 20 alsocomprises a moving acoustic pointer 22 fitted with at least twoultrasound emitters 23. The positioning system 20 also comprises controland processor means forming part of the control unit 16, for example,and serving to cause the ultrasound emitters 22 of the acoustic pointer22 to emit in succession for each position of the pointer relative tothe points of the reference marker, and for each position B₁, B₂, . . ., of the receiver base 14 so as to determine the positions of the pointsof the reference marker in a frame of reference that is associated witheach position of the receiver base in order to determine the positionsin three dimensions of the antenna 4 in a single common frame ofreference.

Implementation of the positioning system 20 for the ultrasound base 14stems from the above description.

The reference structure 21 is placed in stationary manner inside thevolume 2 in which measurements are to be taken. The acoustic pointer 22is placed on a first point P_(i) of the reference marker. In thisposition, the first ultrasound emitter 23 of the pointer is caused toemit so that the ultrasound receiver base 14 determines its position inthree dimensions, as described above. The second ultrasound emitter 23of the acoustic pointer 22 is then caused to emit so that the ultrasoundreceiver base 14 likewise determines its position in three dimensions.Given that the distance between the two emitters 23 of the acousticpointer is known, as is the distance between one of the ultrasoundemitters 23 and the end of the pointer in contact with the point P_(i)of the reference marker, the ultrasound receiver base 14 can determinethe coordinates of the first point P_(i) of the reference marker. Inconventional manner, the ultrasound receiver base 14 calculates thecoordinates using a position-finding or an interferometric method.

The acoustic pointer 22 is then placed on the second point P_(i) of thereference marker and the acoustic acquisition stage as described aboveis performed so as to determine the coordinates of the second pointP_(i) of the reference marker. This stage is repeated for the thirdposition of the acoustic pointer 22 placed relative to the third pointP_(i) of the reference marker.

At the end of this acquisition stage, the positions in three dimensionsof the points P_(i) of the reference marker are determined in a frame ofreference associated with a position B₁ of the ultrasound receiver base14.

It is thus possible to perform one or more acoustic acquisitions asdescribed above, moving the antenna 4.

When measurements need to be performed outside the acoustic line ofsight of the ultrasound receiver base 14 placed in its first positionB₁, provision can be made to move the ultrasound receiver base 14 into asecond position B₂ as shown in FIG. 5. In this second stationaryposition B₂, the acoustic pointer 22 is placed on a point P_(i) of thereference marker and each ultrasound emitter 23 is caused to emit insuccession so as to enable the position of each point P_(i) of thereference marker to be determined using the ultrasound receiver base 14in the manner described above. The acoustic pointer 22 is moved asdescribed above so as to take up the other two points P_(i) of thereference marker in succession, with each ultrasound emitter 23 beingcaused to emit in succession. The ultrasound receiver base 14 thusenables the positions of the points P_(i) of the reference marker to bedetermined in three dimensions in another frame of reference associatedwith the second position B₂ of the ultrasound receiver base 14.Knowledge of the positions of the points P_(i) of the stationaryreference marker in the two frames of references that are associatedwith the ultrasound receiver base 14 makes it possible to deduce amatrix for converting between the positions of the base 14. Thecoordinates of the microphones 5 can thus be expressed in a single frameof reference even when the ultrasound receiver base 14 has been moved.Naturally, the ultrasound receiver base 14 could be moved several times.In addition, it could be envisaged that the fixed reference structure 20comprises a plurality of reference markers that are separated from oneanother by known distances.

The invention is not limited to the examples described and shown sincevarious modifications can be made thereto without going beyond the ambitof the invention.

1. An acoustic measurement installation, characterized in that itcomprises: acoustic measurement instrumentation (3) comprising inparticular an acoustic measurement antenna (4) fitted with at least onemicrophone (5); a positioning system (11) for positioning the antenna(4) by ultrasound, the positioning system comprising: at least oneultrasound emitter (12) mounted on the antenna at a known distancerelative to the microphone; and an ultrasound receiver base (14) forreceiving the signals emitted by each emitter and adapted to determinethe position of each emitter in three dimensions; and a control unit(16) for controlling the positioning system (11) for positioning theantenna (4) and the acoustic measurement instrumentation (3), thecontrol system being adapted during a first stage to cause each emitter(12) to emit in succession in order to determine the position of theantenna in three dimensions, and during a second stage to cause themicrophones (5) to perform acquisition in order to implement acousticmeasurement using the measurement instrumentation.
 2. An acousticmeasurement installation according to claim 1, characterized in that theacoustic measurement antenna (4) is fitted with an ultrasound emitter(12) when it comprises one microphone (5), with at least two ultrasoundemitters (12) when it comprises a series of microphones (5) disposedlinearly, with at least three ultrasound emitters (12) when it comprisesa series of microphones (5) disposed in a plane, and with at least fourultrasound emitters (12) when it comprises a series of microphones (5)disposed in a volume.
 3. An acoustic measurement installation accordingto claim 1, characterized in that each ultrasound emitter (12) ismounted on the antenna (4) on a moving support (71) for adjusting theaxis of the emitter relative to the ultrasound receiver base.
 4. Anacoustic measurement installation according to claim 1, characterized inthat the acoustic measurement antenna (4) is fitted with a member (9)for holding the antenna in position, which member is mounted to moverelative to the antenna.
 5. An acoustic measurement installationaccording to claim 1, characterized in that it includes a system (20)for positioning the receiver base (14), the system comprising: a fixedreference structure (21) defining at least one reference marker with atleast three points (Pi); a moving acoustic pointer (22) fitted with atleast two ultrasound emitters (23); and control and processor meansadapted to control the ultrasound emitters (23) of the acoustic pointer(22) to emit in succession for each position of the pointer relative tothe three points (Pi) of the reference marker and for each position ofthe receiver base (14) so as to determine the positions of the points ofthe reference marker in a frame of reference associated with eachposition of the receiver base, in order to be able to determine thepositions of the antenna in a single frame of reference.
 6. A method ofacoustically measuring a sound source, the method being characterized inthat it comprises the following steps: fitting an acoustic measurementantenna (4) comprising at least one microphone (5) with at least oneultrasound emitter (12) mounted at a known distance from the microphone(5); placing the acoustic measurement antenna (4) in a position that isstationary relative to the sound source; placing an ultrasound receiverbase (14) to face the antenna (4), the receiver base being adapted toreceive an ultrasound signal emitted by the ultrasound emitter (12) andto determine the position of the emitter (12); causing each ultrasoundemitter (12) to emit in succession so as to enable the ultrasoundreceiver base (14) to determine the position of each emitter (12) andconsequently of each microphone (5); and after the end of the stage ofcausing all of the ultrasound emitters (12) to emit, controlling themicrophones (5) to operate in acquisition so as to perform the acousticmeasurement of the sound source.
 7. A method according to claim 6,characterized in that it comprises the following steps: placing areference structure (21) in a stationary position, the structuredefining at least one reference marker having at least three points(Pi); and causing each ultrasound emitter (23) of an acoustic pointer(22) fitted with at least two emitters (23) to emit in succession, andto do so for each position of the pointer (22) placed on each point (Pi)of the reference marker so as to enable the positions of the points ofthe reference marker to be determined in a frame of reference associatedwith the position of the ultrasound receiver base (14).
 8. A methodaccording to claim 7, characterized in that it comprises the followingsteps: moving the ultrasound receiver base (14) to place it in a secondstationary position; causing each ultrasound emitter (23) of the pointer(22) for each position of the pointer placed on each reference point(Pi) of the reference marker to emit in succession in such a manner asto enable the positions of the points of the reference marker to bedetermined in another frame of reference associated with the secondposition of the ultrasound receiver base; and on the basis of thepositions of the points of the reference marker for the first and secondpositions of the ultrasound receiver base (14), determining thepositions of the microphones (5) in a single frame of reference.
 9. Amethod according to claim 6, comprising determining the position of theemitter (12) using a direction-finding method or an interferometicmethod.